\begin{tikzpicture}[
    river/.style={decorate, decoration={random steps,segment length=3pt,amplitude=2pt}},
]
    \tkzDefPoints{0/0/A, 3.9/0/B}
    \tkzDefTriangle[two angles=47 and 80](A,B)  \tkzGetPoint{C}
    \tkzDefTriangle[two angles=87 and 41](A,B)  \tkzGetPoint{D}
    \tkzDrawSegments[thick](A,B  C,D)
    \tkzDrawPolygon[dashed](A,C,B,D)
    \extkzLabelAngel[0.4](B,A,C){$1$}
    \extkzLabelAngel[0.5](C,A,D){$2$}
    \extkzLabelAngel[0.4](D,B,A){$3$}
    \extkzLabelAngel[0.5](C,B,D){$4$}
    \tkzLabelPoints[left](A,D)
    \tkzLabelPoints[right](B,C)

    \begin{scope}[xshift=-.5cm, yshift=1.1cm]
        \foreach \x in {1, ..., 5} {
            \coordinate (X) at (0, \x/5);
            \draw [river]
                (X) to [out=10, in=160] +(2.5, -0.1)
                to [out=10, in=170] +(5, 0.3);
        }
    \end{scope}
\end{tikzpicture}

